Water trampolines can provide hours of fun and entertainment for kids of all ages and even adults. The downside is that many of the best models cost a small fortune to purchase brand new from a retail outlet. Avoid the high cost by making your own water trampoline out of a regular one. The conversion can be done in a few hours with the right tools and supplies.
Remove the jumping pad from the existing trampoline. You will not need the springs anymore, so it doesn't matter if your trampoline is missing them. The pad should be fully intact with no rips, tears, holes, or other damage. Use the protectant to cover the entire surface of the pad. Choose a product that protects against ultraviolet rays and has strong waterproofing capability.
Inflate the inner tubes and use the nylon rope to cinch the sides in so there are no holes left in the middle. Use short lengths of rope cut with the scissors. Tie these inner tubes together with the same rope in a full, tight circle sized just smaller than the pad. The edges of the pad should touch the ground when you place it over this inflated circle. If you have a smaller trampoline, you may only need one truck tire inner tube. Also, if you have a larger pad, you can look for a huge inner tube from a giant tire. That way you only have to work with one tube for the whole project.
Cut the hooks off all your bungee cords. You will need equal lengths of cord for every grommet on the pad. Tie one end of each cord in a strong knot to the grommet fitting and loop the cord all the way around the ring of inner tubes. Tie the other end tightly around the tube ring to create a strong attachment point. Repeat this process for the entire circle, securing every grommet to the tubes. Wrap the pad around the edge of the tube ring tightly enough so that jumping on the trampoline will not allow the pad to slip off.
Tie bungee cords to four equidistant points on the tube ring. Drill holes in the ends of your PVC pipe lengths, which should be equal to the diameter of your circle. The holes should be large enough for the bungee cord to pass through. Thread the four bungee cords through the four holes, keeping the pipes on the underside of the tire ring. Tie a knot around the entire pipe and leave enough excess cord so you can tie the ends together in one junction without causing the pipes to bend. Attach this junction to an anchor rope.
Bring the trampoline out to at least 8 feet of water that is at least 30 feet away from any dock. Tie the anchor rope to an anchor or a few cinder blocks. You might also be lucky enough to find an old mooring block that's not in use anymore. Whatever anchor you use, position it directly underneath the raft and make it tight enough to prevent any drifting.
Check junkyards or the free section of craigslist for your inner tubes and the trampoline. This can save you even more money, which you can spend to buy a new trampoline pad and/or a set of tire tubes.
If you use a single tire you will not need the PVC pipes to keep the makeshift inner tube circle intact.